In a radio communication system such as a cell phone system or the like, a radio base station (for example, an eNB: e NodeB) performs radio communication with a mobile terminal (for example, a UE: User Equipment) which is positioned in a cell that the radio base station contains. An inherent cell identifier (for example, a PCI: Physical Cell Identifier) that may not collide with (that is, may not overlap) those of neighboring cells is allocated to each cell that each radio base station contains such that each mobile terminal is allowed to identify each cell. For example, in the case that one cell identifier is allocated to one cell that one radio base station contains, another cell identifier which is different from one cell identifier is allocated to another cell that one radio base station or another radio base station contains and neighbors one cell.
In recent years, the proposal of SON (Self Organization Network) is being promoted aiming at cost reduction of a radio communication system maintaining operation including a cell identifier allocating operation. For example, as one of techniques of the SON that automatically constructs a neighbor relation between cells including the cell identifier allocating operation, ANR (Automatic Neighbor Relation) is proposed. In the ANR, an ECGI (Evolved Cell Global Identifier) corresponding to a cell identifier (PCI) concerned is notified from a mobile terminal to a radio base station utilizing “Measurement Report” that informs a radio base station of the cell identifier (PCI) that the mobile terminal has recognized. The radio base station that has received notice of the ECGI grasps the presence of an unknown cell or an unknown radio base station and constructs a neighbor relation with reference to both the ECGI and the PCI.
Japanese Laid-open Patent Publication No. 2008-199223 is one example of related art. 3GPP TS36. 423 v9. 1. 0 is another example of related art.
In the ANR, it is preconditioned that cell identifiers do not collide with one another among a plurality of neighboring cell. That is, in the ANR, it is preconditioned that unique cell identifiers are respectively allocated to a plurality of neighboring cells. However, it may sometimes occur that the cell identifiers collide with one another depending on an actual operation state of a radio communication system concerned. Collision of the cell identifiers may adversely affect automatic construction of the neighbor relation among the cells by the ANR.
Next, a case in which a new radio base station is to be installed in a blind zone which is present in an arbitrary area where an existing radio base station (or an existing cell) has already been installed will be studied by way of example. The existing radio base station may be possibly installed as a stand-alone radio base station that may not consider the uniqueness of each cell identifier. Therefore, a newly installed radio base station (or a cell that the newly installed radio base station contains) may possibly construct a neighbor relation with the existing radio base station (or the existing cell) that contains a cell to which the same cell identifier as that of the cell in which the newly installed radio base station is allocated. In the case that the cell identifiers collide with each other, both the radio base stations the cell identifiers of which collide with each other may possibly change their cell identifiers because appropriate procedures are not defined by the ANR. Or, the cell identifier in one radio base station which is larger than the other radio base station in processing load imposed on changing of its cell identifier in the radio base stations the cell identifiers of which collide with each other may possibly be changed.
Or, such a situation may be also estimated that although two existing radio base stations have not been in a neighbor relation so far owing to presence of an obstacle (a shield) such as a building or the like between them, these two existing radio base stations are newly brought into the neighbor relation owing to removal of the obstacle between them. In the above mentioned situation, in the case that the cell identifiers collide with each other between the two existing radio base stations, it may be difficult to distinguish these two radio base stations from each other using cell identifiers allocated thereto. Accordingly, in the ANR, it may be difficult to automatically construct the neighbor relation of cells between two radio base stations.